This invention relates to cartons which are subjected to loads from stacking. An example is for transporting produce, e.g., strawberries and grapes, in stacked loads.
The cost of transporting produce from the fields to the ultimate consumer is partially determined by the gross weight of what is being shipped. Since it costs just as much per pound to transport the cartons in which the produce is shipped as the produce itself, it is desirable that the cartons weigh as little as possible. For this reason, and due to corrugated paper's strength and low cost, packaging produce in corrugated cartons has become the preferred mode of transporting fresh produce.
Since the cost of transporting the produce to market is also partially determined by the amount of floor space taken up by the produce, it is necessary that these cartons be placed in relatively tall stacks. This means that the cartons at the bottom of the stacks must be able to support the weight of virtually the entire stack of cartons. Furthermore, when the vehicle transporting the produce turns or sways, the inertia of the cartons causes the stacks to twist and sway. Since the stacks are held stationary only at the bottom, the twisting and swaying of the stacks causes a disproportionately large amount torque to be applied to the walls of lower cartons.
The produce being transported is often quite wet and the moisture from the produce has a tendency to gradually saturate the corrugated cartons. When this occurs, the load and torque-bearing capacity of the corrugated cartons greatly diminishes. In this state, the weakened upper corners of the cartons have a tendency to distend outward, thereby allowing the weight of the cartons stacked above to force the carton formerly supported by the corners to slide into the lower carton and damage the produce contained therein. The twisting of the stacks may also cause the relatively weak end of one of the wetted cartons to twist and misshapen, allowing the weight of the cartons stacked above to crush the produce in the carton. In the worst case, the saturated corner of one of the lower cartons could so weaken that it completely buckles, thereby removing one of the corner supports from the stack and potentially causing the entire stack to tumble over.
In light of the problems involved in transporting wet produce in corrugated cartons, it is desirable that the cartons be reinforced in some manner. It is important, however, that the means utilized to reinforce the corrugated cartons not add significantly to the weight, bulk, or cost of the cartons.
Since it is envisioned that large quantities of the reinforced cartons will need to be assembled, it is important that the carton design lend itself to simple and inexpensive mass production techniques. The corrugated portion of the carton should preferably be as simple as possible so that the the number of cutting operations necessary to make it is minimized. Likewise, the reinforcing means itself should be relatively inexpensive to manufacture. It is also desirable, in order to minimize inventory problems, that the reinforced corrugated design incorporate a minimum number of parts, and that these parts be as light and as compact as possible for easy handling and storage.
The process of assembling the reinforced corrugated cartons ought to be as simple as possible. Every step in the process should be simple enough that it can be performed by machine. Finally, although the corrugated portion of the reinforced boxes typically will be destroyed by the moisture from the produce, it is desirable that the reinforcing means be recycled, in order that material costs can be minimized.
Necessarily, the recycling process will only be cost effective if the used boxes can be simply and easily disassembled. Preferably, the disassembling process should be able to be performed without tools of any kind and without the necessity of undue care being taken in order ensure that the reinforcing means is not damaged. The reinforcing means should also be relatively light and compact so that the cost involved in transporting the reinforcing means from the market to the carton assembly location is not prohibitive.
What is needed is a simple and effective means of reinforcing corrugated produce cartons so that they, even when wet, will be able to support the weight of the cartons stacked above them, and bear the torque applied upon them due to the twisting and swaying of the stacked cartons.